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If by radiation all nitrogenase enzyme are inactivated, then there will be no :-
A
Fixation of atmospheric nitrogen
B
Conversion from nitrate to nitrite in legumes
C
Conversion from ammonium to nitrate in soil
D
Fixation of nitrogen in legumes
Detailed Solution
Nitrogenase is the enzyme that reduces atmospheric nitrogen to ammonia in biological nitrogen fixation:
$N_2 + 8e^- + 8H^+ + 16ATP \xrightarrow{nitrogenase} 2NH_3 + H_2 + 16ADP + 16P_i$
In legumes, nitrogen fixation takes place in the root nodules formed by Rhizobium, where nitrogenase is protected from oxygen by leghaemoglobin.
If all nitrogenase is inactivated, the fixation of nitrogen in legumes will stop.
Conversion of nitrate to nitrite is done by nitrate reductase, and conversion of ammonium to nitrate in soil (nitrification) is done by Nitrosomonas and Nitrobacter. These processes do not need nitrogenase, so they will continue.
So, as per the answer key, there will be no fixation of nitrogen in legumes. (Biological fixation of atmospheric nitrogen by free-living microbes would also stop, but nitrogen is still fixed by lightning and industrial processes, which do not use nitrogenase.)
$N_2 + 8e^- + 8H^+ + 16ATP \xrightarrow{nitrogenase} 2NH_3 + H_2 + 16ADP + 16P_i$
In legumes, nitrogen fixation takes place in the root nodules formed by Rhizobium, where nitrogenase is protected from oxygen by leghaemoglobin.
If all nitrogenase is inactivated, the fixation of nitrogen in legumes will stop.
Conversion of nitrate to nitrite is done by nitrate reductase, and conversion of ammonium to nitrate in soil (nitrification) is done by Nitrosomonas and Nitrobacter. These processes do not need nitrogenase, so they will continue.
So, as per the answer key, there will be no fixation of nitrogen in legumes. (Biological fixation of atmospheric nitrogen by free-living microbes would also stop, but nitrogen is still fixed by lightning and industrial processes, which do not use nitrogenase.)